#include <iostream>
#include <vector>
using namespace std;
 
int main()
{
    vector<long long> dp(21, 0);
    dp[2] = 1;
    for(int i = 3; i < 21; ++i)
    {
        dp[i] = (i - 1) * (dp[i - 1] + dp[i - 2]);
    }
 
    int n = 0;
    while(cin >> n)
    {
        cout << dp[n] << endl;
    }
    return 0;
}